1. Field of Endeavor to which the Invention Pertains
The present invention relates to radiation detectors and, more particularly, to a radioactivity distribution detection system which has cross section openings larger than the intrinsic resolution of the detector and at least two openings of different shape.
2. Description of Prior Art
Various types of radioactivity distribution detection systems have become known in the art for determining the location of radioactive material injected in diagnostic amounts into a human or an animal body. These systems based on the gamma camera of the Anger type (U.S. Pat. No. 3,011,057) have proven to be of limited sensitivity (10-4) and limited resolution compared to the intrinsic resolution of the detector. Moreover the use of such systems to realize tomography degrades further the spatial resolution of the system. The purpose of tomography is to realize sections of the object emitting the radiation. Tomography of an object emitting gamma rays is also called single photon emission tomography (SPECT). SPECT is different from positron emission tomography (PET) where two photons are simultaneously emitted by the radionuclid. This property permits a coincidence detection, without collimator. The subject of the present invention is a tomographic imaging system able to give a section of the radiation emitter whatever the radiation emitted. This system applies well to gamma rays but it can also apply to X-rays, UV, IR any photons or small particles like neutrons, electrons, or any radiation travelling in straight lines. We proposed to increase the bore hole of the collimator beyond the value of the intrinsic resolution of the detector, and to add a scanning movement of the collimator, in order to get sufficient data (U.S. Pat. No. 5,448,073 Jeanguillaume September 1995). Although this system provides an improvement compared to the conventional system the noise limits slightly the resolution and the accuracy of the reconstructed images. The time of the reconstruction program is another limitation of the system.
It is the object of the present invention to provide some improvements of the high sensitivity gamma camera proposed in the U.S. Pat. No. 5,448,073 C. Jeanguillaume September 1995. The principal improvement is to associate at least two openings of different shape in the collimator, which allows a more complete knowledge of the data to be acquired, and a fast deconvolution algorithm to be performed. A better image and a faster reconstruction time can then be achieved. Another improvement is to describe different physical arrangements to realize the scanning movement necessary to the system. The practical arrangements of linear and orbital movement described herein provide a faster and more complete acquisition.